Optical fiber can be used in various applications and, like many other optical media, optical fiber exhibits nonlinear optical effects. Nonlinear optical effects in optical fiber can lead to undesired consequences, such as optical signal distortions in fiber optical networks. On the other hand, nonlinear optical effects in optical fiber can also be advantageously used to achieve certain beneficial technical results for various applications. For example, four wave mixing effects in optical fiber can be used for certain signal processing and for generation of frequency-shifted coherent signals, including constructing fiber-based optical parametric amplifiers and optical parametric amplifiers.